Could be crashing of Browser Hard drive related?

I had for weeks safari crashing.Think it started around the time i started useing
File Vault.But firefox worked well.
now i use another Hard Drive. also leopard on as on the other.On that Hard drive works Safari excelent,but Firefox is doing just nothing.Got me TenForFox on but also not doing well.Youtube now just on Safari running,and on Previous HD on firefox.
Have 2 Gb ram and works fine.Sometimes is it overworked and slows down,but after a Re-Start runs as New.
Its a 1.25 ghz MDD with Free sophos on which gave me twice Alarm when i tryed doing around with Firefox.
think it has to do which update is on the HD.not just just the Browser but maybe also adobe Flash.
tryed HTML5 but come not forward with finding anything the Mac would accept.

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